The invention concerns a method for stabilizing the movement of an articulated chain of a chain block, especially for preventing the formation of a resonance oscillation of the chain, in which an articulated chain is passed across a polygonal chain wheel with non-uniform pitch, which is actuated by an electric motor. The invention also concerns a chain block with a chain taken across a polygonal chain wheel and with an electric motor acting on the chain wheel.
From German patent application DE 1 531 307 A1 there is known a chain block with electric motor actuation. The chain block essentially consists of a chain wheel, actuated by the electric motor, across which is passed the chain, especially a round steel chain, with a means of picking up the load. The chain wheel in this case is configured as a so-called pocket wheel, whose pockets are form-fitted to the links of the chain in order to transmit the lift forces. There is an alternation of one horizontal and one vertical link as they come off the chain wheel. In keeping with the curvature ratio of the chain, the chain wheel has a non-uniform polygonal circumference. This polygonal circumference of the chain wheel means that, as the chain comes off from the chain wheel, the effective radius of the chain wheel changes as a function of angle, and thus the speed of the chain periodically fluctuates accordingly. Thus, the periodic fluctuations even occur when the electric motor has constant speed. This entails an unstable running of the chain, a continual pulsating load on the chain block, and possible troublesome resonance effects.
In order to diminish the fluctuations in the speed at which the chain comes off the chain wheel, it is known how to configure the driven gear arranged at the electric motor and the driving gear of the chain wheel, meshing together, each in a shape deviating from the circular, i.e., non-round, in order to let the speed of the chain wheel pulsate and counteract the above-described polygon effect.
These mechanically operating equalization systems can only result in limited moderating of the run-off speed of a chain of a chain block, since only the low-order mathematical elements of the polygon effect are taken into account. Furthermore, these mechanically operating equalization systems require a large structural expense.
Moreover, from German patent application DE 199 58 709 A1 there is a known method and a device for reducing the polygon effect in the deflection zone of people conveyor systems, especially escalators or moving pavements. The people conveyor systems have an endless plate link chain or Gall's chain, which circulates between two deflection wheels and is taken away rolling at least in the region of its upper side. The plate link chain or Gall's chain and also the deflection wheels are characterized by a uniform pitch. One of the two deflection wheels is driven by an electric drive. In order to reduce the polygon effect occurring as the plate link chain runs around the deflection wheels, a different speed is superimposed on the speed of the deflection wheel. As a result, the electric drive is actuated by a frequency converter so that it turns at a non-constant speed. A regulating device associated with the frequency converter processes the phase position of the deflection wheel and/or the speed of the chain as input signals.
A further modification of the above-described device for reducing the polygon effect in the deflection region of people conveyor systems, especially escalators or moving pavements, is known from German Patent DE 101 20 767 C2. Here, a position-dependent control of the speed of the chain is provided in that the speed fluctuations occurring on the chain segment, when driven by essentially constant rotational frequency, are determined. It is then proposed to accomplish an equalization of the detected speed fluctuations by operating the deflection wheel with non-uniform frequency of rotation, for which a mathematical function is determined that is synchronized only with the angular position of the deflection wheel in the operating state.
The above-described methods and devices for reducing the polygon effect in the deflection region of people conveyor systems pertain to an endless plate link chain. This plate link chain normally has a fixed length, a uniform pitch, and is supported at least in the region of the working side. The polygon effect which occurs is thus dependent on the uniform pitch of the chain wheel. Because the plate link chain is supported at least in the region of the plate link, it experiences a strong dampening. Furthermore, the polygon effect which occurs and which is supposed to be reduced is easier to manage, thanks to the fixed length of the plate link chain.